5 Steps to a 5 AP Chemistry 2019

250 ❯ STEP 4. Review the Knowledge You Need to Score High

For example, if liquid titanium(IV) chloride (acidified with HCl) is electrolyzed by a

current of 1.000 amp for 2.000 h, how many grams of titanium will be produced?

Answer:

TiCl(l) 42 →+Ti(s)2Cl(g) (not necessary)

Ti4eTi 

4 +−+→ (necessary)

(2.000h)

3,600 s

h

1.000C

s

1molee

96,485 C

1moleTi

4molee

47.90gTi

molTi

0.8936gTi









































=

−

−

Calculation of E°cell also allows for the calculation of two other useful quantities—the

Gibbs free energy (DG°) and the equilibrium constant (K).

The Gibbs free energy is the best single thermodynamic indicator of whether a reaction

will be spontaneous (review the Thermodynamics chapter). The Gibbs free energy for a

reaction can be calculated from the E° of the reaction using the following equation:

∆°Gn=−FE°cell

where F is Faraday’s constant of 96,500 C/mol e- = 96,500 J/V mol.

0.48 V

Voltmeter

Salt bridge Salt bridge

e− e− e− e−

Sn

Sn Sn2+

Cu2+

2e− 2e−

Cu

Cu

Anode

(–)

Cathode

(+)

Cu

Cu Cu2+

Sn2+

2e− 2e−

Sn

Sn

Anode

(+)

Cathode

(–)

Oxidation half-reaction

Sn(s) Sn2+(aq) + 2e−

Cu2+(aq) + 2e− Cu(s)

Reduction half-reaction

Sn(s) + Cu2+(aq) Sn2+(aq) + Cu(s)

Overall (cell) reaction

Oxidation half-reaction

Cu(s) Cu2+(aq) + 2e−

Cu(s) + Sn2+(aq) Cu2+(aq) + Sn(s)

Sn2+(aq) + 2e− Sn(s)

Reduction half-reaction

Overall (cell) reaction

External source

greater than 0.48 V

Figure 16.2 Comparison of a galvanic cell (left) and an electrolytic cell (right).